For many years, it has been known and also been a practice to place voids, particularly cardboard and styrofoam voids, in concrete beams during the formation process. Voids in a concrete beam make the beam lighter without any decrease in effective strength, and are overall very cost effective inasmuch as the presence of such voids decrease concrete and reinforcing steel requirements.
In forming a concrete beam with a void, it is necessary to strategically place the void within the overall beam structure. This is customarily accomplished by employing a void hold down device within the beam structure itself. Once concrete is poured within the form structure, the voids will tend to rise. Therefore, it is important that the void hold down devices be particularly positioned above the voids so as to appropriately limit the vertical rising movement of the voids during casting.
It is known in the prior art to utilize an open wire steel-type void hold down device. The wire steel hold down device is shaped so as to surround an upper portion of the void and includes an open top band structure. The wire steel hold down device includes a central coupling section that extends upwardly from the base or band and engages the void. This coupling section is formed of wire steel itself and is threaded so as to receive the lower end portion of a hold down rod that is adjustably supported about an overhead structure that extends across and over the concrete form. There are numerous disadvantages and drawbacks to these wire steel void hold down devices. First, they are relatively expensive. Secondly, because all voids are a source of oxygen and moisture, there is natural tendency for corrosion of any ferrous material in permanent contact. Internal corrosion can lead to future durability failure. Additionally, because of the nature of the wire steel, these types of void hold down devices tend to corrode easily and this makes it difficult to extract the hold down rod from these devices once the concrete beam has been cured. In this same regard, the structure that joins the hold down device is formed by spirals of wire and because of that is somewhat open to concrete passing through such structure and becoming embedded in and around the hold down rod. This also makes it more difficult for the hold down rod to be extracted from the wire steel hold down device.
Another drawback to the wire steel type hold down device is that its sleeve coupling that attaches to a down rod is completely open through the bottom. This enables the wire steel hold down device to be threaded up the down rod leaving the lower end of the down rod exposed. The problem presented here is that it is very easy for the wire steel hold down devices to be incorrectly spaced on the down rods resulting in the voids being mispositioned within the beam structure. In particular, it is possible for the wire steel hold down device to assume a position midway the down rod and for the underlying void to be pierced by the lower end of the down rod and to assume an improper final position within the concrete beam.
In addition, the wire steel hold down devices are difficult to use and often time consuming to install. Such wire steel hold down devices are not very versatile in as much as different sizes are required for different size voids, and because of the nature of the wire steel hold down devices they are not readily available in different sizes.
Therefore, there is and continues to be a need for a cost effective, non-corrosive and easy to use void hold down device.